In recent years, along with a development in wireless techniques, a wireless ad-hoc network is desired to realize in cognitive radio or multi-channel/multi-interface (referred to as MCH/IF below) environments.
The wireless ad-hoc network in the MCH/IF environment contains, as a node, a communication terminal including a plurality of wireless interfaces to which bands (channels) with different communication properties are assigned.
How to assign the channels to the wireless interfaces may employ some aspects. For example, there may be employed an aspect in which a plurality of channels is assigned to one wireless interface and the wireless interface instantaneously switches to a proper channel on communication. There may be employed an aspect in which one channel is assigned to one wireless interface and the same channel keeps being used during a certain period.
There will be described, in the following description, an example in which one channel is assigned to one wireless interface. In this case, to select a wireless interface used for communication means to select a channel.
A property of a communication link forming the MCH/IF topology is largely different depending on whether the band used for the wireless interface is high or low. For example, for the VHF or UHF band with a low frequency, long-distance communication is possible but a communication capacity is limited to several hundred kbps (bit per second). On the other hand, for the SHF band with a high frequency of 3 GHz or more, the capacity ranges from several Mbps to several hundred Mbps but the communication range is narrowed to several hundred meters to several tens meters.
The communication terminal uses a plurality of wireless interfaces assigned with different channels. Thus, the number of recognizable neighboring communication terminals is different and the capacity is also different for each wireless interface. A plurality of communication links having different communication properties (capacity or communication range) may be present for the same communication terminal.
Thus, each communication terminal needs to select an optimum channel for a communication path from among the available channels and to construct a communication path according to a communication purpose. FIG. 12 is an explanatory diagram illustrating exemplary channels selected between communication terminals on a communication path. In the example illustrated in FIG. 12, a plurality of consecutive arrows indicate a communication path. The example illustrated in FIG. 12 indicates a case in which any channel of CH1, CH2 and CH3 is selected between the individual communication terminals.
Various policies may be assumed for a channel select policy for the communication terminals on the communication path. For example, there may be assumed a select policy of preferentially selecting a channel with a long propagation distance such that the number of transfers is minimum or a select policy of preferentially selecting a channel with a wide communication capacity. FIG. 13 illustrates an example in which channels are selected according to the former select policy and FIG. 14 illustrates an example in which channels are selected according to the latter select policy. FIG. 13 and FIG. 14 illustrate the examples in which the channels between the communication terminals are selected from the three channels of CH1 to CH3. The communication capacities are assumed to have a relationship of (communication capacity of CH1)<(communication capacity of CH2)<(communication capacity of CH3). The propagation distances are assumed to have a relationship of (propagation distance of CH1)>(propagation distance of CH2)>(propagation distance of CH3). As illustrated in FIG. 13 or FIG. 14, various combinations of channels to be assigned to each link on the communication path are present depending on a channel select policy.
Patent Literature 1 describes therein that a frequency band division pattern in a base station is used in a plurality of bases.
Patent Literature 2 describes therein a method for assigning wireless resources for calculating a delay time, and the like. With the method described in Patent Literature 2, a delay time in one hop section such as between a base station and a terminal is calculated.
Patent Literature 3 describes therein how to calculate a delay time per unit distance.